Display device

ABSTRACT

According to one embodiment, a display device includes a substrate, a switching element provided on the substrate and including a relay electrode, a first electrode provided further away from the substrate than the switching element, a first insulating film provided on the first electrode and having a first thickness, a second electrode provided on the first insulating film, a second insulating film provided on the second electrode and having a second thickness and a third electrode provided on the second insulating film and supplied with a same potential as that of the first electrode. The second thickness is greater than the first thickness.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/279,700 filed Feb. 19, 2019, and is based upon and claims the benefitof priority from Japanese Patent Application No. 2018-027937, filed Feb.20, 2018, the entire contents of each of which are incorporated hereinby reference.

FIELD

Embodiments described herein relate generally to a display device.

BACKGROUND

For example, in liquid crystal display devices, a common electrode and apixel electrode, which oppose each other while interposing an insulatinglayer, form a capacitor to holding the potential applied to a liquidcrystal layer. In recent years, as the size of the liquid crystaldisplay devices is drastically reduced, the area of the pixel electrodeis accordingly reduced. Under these circumstances, as the downsizingfurther progresses, it becomes difficult to form a sufficient capacitorin each pixel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a basic structure and an equivalentcircuit of a display device according to the first embodiment.

FIG. 2 is a plan view showing a configuration example of a switchingelement SW shown in FIG. 1.

FIG. 3 is a cross section taken along line III-III shown in FIG. 3.

FIG. 4 is a plan view showing a configuration example of a firstelectrode E1 shown in FIG. 3.

FIG. 5 is a plan view showing a configuration example of a secondelectrode E2 shown in FIG. 3.

FIG. 6 is a plan view showing a configuration example of a thirdelectrode E3 shown in FIG. 3.

FIG. 7 is a plan view showing an example of arrangement of the firstelectrode E1, the second electrode E2, and the third electrode E3 with apotential supply line 6 shown in FIG. 1.

FIG. 8 is a cross section taken along line VIII-VIII shown in FIG. 7.

FIG. 9 is a plan view of a first modified example of the firstembodiment.

FIG. 10 is a plan view of a second modified example of the firstembodiment.

FIG. 11 is a plan view of a third modified example of the firstembodiment.

FIG. 12 is a plan view of a second electrode E2 in the third modifiedexample of the first embodiment.

FIG. 13 is a plan view of a third electrode E3 in the third modifiedexample of the first embodiment.

FIG. 14 is a cross section of a fourth modified example of the firstembodiment.

FIG. 15 is a cross section of a display device according to the secondembodiment.

FIG. 16 is a plan view showing a configuration example of a firstelectrode E1 shown in FIG. 15.

FIG. 17 is a plan view showing a configuration example of a secondelectrode E2 shown in FIG. 15.

FIG. 18 is a plan view showing a configuration example of a thirdelectrode E3 shown in FIG. 15.

FIG. 19 is a plan view showing an example of arrangement of the firstelectrode E1, the second electrode E2, and the third electrode E3 with apotential supply line 6 shown in FIG. 1.

FIG. 20 is a cross section taken along line XX-XX shown in FIG. 19.

FIG. 21 is a plan view of a first modified example of the secondembodiment.

FIG. 22 is a plan view of a second modified example of the secondembodiment.

FIG. 23 is a plan view of a third modified example of the secondembodiment.

FIG. 24 is a plan view of a first electrode E1 in the third modifiedexample of the second embodiment.

FIG. 25 is a plan view of a third electrode E3 in the third modifiedexample of the second embodiment.

DETAILED DESCRIPTION

In general, according to one embodiment, a display device comprises asubstrate, a switching element provided on the substrate and including arelay electrode, a first electrode provided further away from thesubstrate than the switching element, a first insulating film providedon the first electrode and having a first thickness, a second electrodeprovided on the first insulating film, a second insulating film providedon the second electrode and having a second thickness and a thirdelectrode provided on the second insulating film and supplied with asame potential as that of the first electrode, and the second thicknessis greater than the first thickness.

The embodiments will be described hereinafter with reference to theaccompanying drawings. Note that the disclosure is presented for thesake of exemplification, and any modification and variation conceivedwithin the scope and spirit of the invention by a person having ordinaryskill in the art are naturally encompassed in the scope of invention ofthe present application. In addition, in some cases, in order to makethe description clearer, the widths, thicknesses, shapes, etc., of therespective parts are schematically illustrated in the drawings ascompared to the actual modes. However, the schematic illustration ismerely an example, and adds no restrictions to the interpretation of theinvention. Moreover, in the specification and drawings, the structuralelements, which have functions identical or similar to the functionsdescribed in connection with preceding drawings, are denoted by likereference numbers, and an overlapping detailed description thereof isomitted unless otherwise necessary.

First Embodiment

FIG. 1 is a plan view showing a basic structure and an equivalentcircuit of a display device according to the first embodiment. In thefigure, a first direction X and a second direction Y are directionsintersecting each other, and a third direction Z is a directionintersecting the first direction X and the second direction Y. Forexample, the first direction X, the second direction Y and the thirddirection Z are orthogonal to each other, but they may cross each otherat an angle other than 90 degrees. In this specification, the directiontowards the tip of the arrow which shows the third direction Z isreferred to as “up”, and the direction which goes conversely from thetip of the arrow is referred to as “down”. Further, when it is assumedthat an observation position at which the display device DSP is to beobserved is located at the pointing end side of the arrow indicating thethird direction Z, a view toward an X-Y plane defined by the firstdirection X and the second direction Y is referred to as a plan view.

A display device 1 comprises a display panel 2. The display panel 2 is,for example, a liquid crystal display panel. In the example illustrated,the display panel 2 is approximately rectangular, and includes endportions 2Xa and 2Xb extending along the first direction X, and endportions 2Ya and 2Yb extending along the second direction Y. The displaypanel 2 comprises a first substrate SUB1, a second substrate SUB2 and aliquid crystal layer LC. The first substrate SUB1 and the secondsubstrate SUB2 oppose each other and are adhered together via a sealingmaterial. The liquid crystal layer LC is held between the firstsubstrate SUB1 and the second substrate SUB2, and functions as a displayelement. The display panel 2 includes a mounting portion 201 in whichthe first substrate SUB1 extends further from the second substrate SUB2.In the example illustrated, the mounting portion 201 is formed along theend portion 2Xa.

The display panel 2 includes a display area DA which displays images anda non-display area NDA located on an outer side of the display area DA.The display area DA is located in a region where the first substrateSUB1 and the second substrate SUB2 overlap each other, and is equivalentto the region where the liquid crystal layer LC is provided. In theexample illustrated, the non-display area NDA is formed into a frameshape which surrounds the display area DA.

The display panel 2 comprises a plurality of scanning lines G and aplurality of signal lines S in the display area DA. In the exampleillustrated, the scanning lines G extend along the first direction X,and are arranged along the second direction Y at intervals. The signallines S extend along the second direction Y, and are arranged along thefirst direction at intervals. Further, the display panel 2 comprisespixels PX respectively in vicinities of intersections between thescanning lines G and the respective signal line S. Here, a pixel PX isequivalent to a minimum unit individually controllable with respect toan image signal. In the example illustrated, the pixels PX are arrangedin a matrix along in the first direction X and the second direction Y.

Each pixel PX comprises a switching element SW, a pixel electrode PE, acommon electrode CE and a liquid crystal layer LC. The switching elementSW is electrically connected to a scanning line G and a signal line S. Asignal potential supplied to the signal line S is supplied to the pixelelectrode PE via the switching element SW. The common electrode CE isdisposed over a plurality of pixels PX. The liquid crystal layer LC isdriven by an electric field produced between the pixel electrode PE andthe common electrode CE. In this embodiment, the display area DA isequivalent to the region where the pixel electrode PE is disposed.

The display panel 2 comprises a potential supply line 6 in thenon-display area NDA. In the example illustrated, the potential supplyline 6 is formed into an approximately rectangular shape to surround thedisplay area DA. In other words, the potential supply line 6 surroundsall the pixel electrodes PE. To the potential supply line 6, a commonpotential is supplied via terminal portions TE1 and TE2 formed in themounting portion 201. In this embodiment, the common electrode CEextends to the non-display area NDA, and is connected to the potentialsupply line 6 in the non-display area NDA. In the example illustrated,the common electrode CE extends along the first direction X. Note thatsuch a structure that the potential supply line 6 does not surround apart of the display area DA, that is, for example, the potential supplyline 6 is not formed along a lower side portion (a side on an endportion 2Xa side) of the display area DA, but provided only along thethree remaining sides may as well be adopted.

Further, the display panel 2 comprises a source driver 3, gate drivers 4a and 4 b, a driver IC 5, etc., in the non-display area NDA. The sourcedriver 3, the gate drivers 4 a and 4 b, and the driver IC 5 are locatedon an outer side with respect to the potential supply line 6. Forexample, the source driver 3 is provided between the mounting portion201 and the potential supply line 6. The gate driver 4 a is providedbetween the end portion 2Ya and the potential supply line 6. The gatedriver 4 b is provided between the end portion 2Yb and the potentialsupply line 6. The signal lines S extend to the non-display area NDA,and are connected to the source driver 3. The scanning lines G extend tothe non-display area NDA, and are connected to the gate drivers 4 a and4 b. The driver IC 5 is mounted in the mounting portion 201. The driverIC 5 controls the source driver 3 and the gate drivers 4 a and 4 b.

FIG. 2 is a plan view diagram showing a configuration example of theswitching element SW shown in FIG. 1. The switching element SW is, forexample, a double-gate thin film transistor. The switching element SWincludes a semiconductor layer SC, gate electrodes GE1 and GE2, a relayelectrode RE and the like.

The semiconductor layer SC includes a first portion SC1, a secondportion SC2 and a third portion SC3. The first portion SC1 is locateddirectly under the respective signal line S. The first portion SC1extends along the second direction Y, and intersects the respectivescanning line G. The second portion SC2 is located between signal linesS adjacent to each other. The second portion SC2 extends along thesecond direction Y, and intersects the respective scanning line G. Thethird portion SC3 extends along the first direction X, and connects thefirst portion SC1 and the second portion SC2 to each other. Note that apart of the second portion SC2 and the third portion SC3 are located ina pixel PX adjacent along the second direction Y to a pixel PXcorresponding to the switching element SW.

The semiconductor layer SC is connected to the respective signal line Sin a contact hole CH1. The signal lines S each function as, for example,a source electrode of the respective switching element SW. Further, thesemiconductor layer SC is connected to the relay electrode RE in acontact hole CH2. The relay electrode RE functions as a drain electrodeof the respective switching element SW. The gate electrode GE1 isequivalent to a part of the respective scanning line G, which overlapsthe first portion SC1. The gate electrode GE2 is equivalent to a part ofthe respective scanning line G, which overlaps the second portion SC2.

FIG. 3 is a cross section taken along the line III-III shown in FIG. 2.The first substrate SUB1 comprised an insulating substrate 10, aswitching element SW, insulating films 11 to 15, a first electrode E1, asecond electrode E2, a third electrode E3, an alignment film AL1 and thelike.

In the example illustrated, the switching element SW is a bottom-gatethin film transistor. The switching element SW includes gate electrodesGE1 and GE2, a semiconductor layer SC, and a relay electrode RE1. Thegate electrodes GE1 and GE2 are formed on the insulating substrate 10,and are covered by the insulating film 11. The semiconductor layer SC isformed on the insulating film 11, and is covered by the insulating film12. The signal line S and the relay electrode RE are formed on theinsulating film 12, and are covered by the insulating film (organicinsulating film) 13. In the contact holes CH1 and CH2 which penetratethe insulating film 12, the signal line S and the relay electrode RE areeach in contact with the semiconductor layer SC.

The first semiconductor layer SC is formed of, for example,polycrystalline silicon. The gate electrodes GE1 and GE2, the relayelectrode RE and the signal line S are each formed from, for example, ametal material such as aluminum (Al), titanium (Ti), silver (Ag),molybdenum (Mo), tungsten (W), copper (Cu) and chromium (Cr), or analloy of any combination of these metal materials. The gate electrodesGE1 and GE2, the relay electrode RE, and the signal line S may be of asingle- or multi-layer structure.

The insulating film 13 includes a contact hole (third through hole) CH3which penetrates to the relay electrode RE. The first electrode E1 isformed on the insulating film 13 except for the vicinity of the contacthole CH3. The insulating film (first insulating film) 14 covers thefirst electrode E1 and is formed also on the insulating film 13. A partof the insulating film 14 extends into the contact hole CH3 and uncoversa part of the relay electrode RE. The second electrode E2 is formed onthe insulating film 14. The second electrode E2 is in contact with therelay electrode RE in the contact hole CH3. With this structure, thesignal potential supplied to the signal line S is supplied to the secondelectrode E2 via the relay electrode RE.

The insulating film (second insulating film) 15 covers the secondelectrode SE2. The insulating film 15 is formed also in the contact holeCH3. In the illustrated example, the insulating film 15 is formed alsoon the insulating film 14. The third electrode E3 is formed on theinsulating film 15. For example, the third electrode E3 includes aplurality of openings OP. The openings OP each oppose the secondelectrode E2. The third electrode E3 is covered by the alignment filmAL1. The alignment film AL1 is provided also on the insulating film 15in the openings OP.

The insulating films 11, 12, 14 and 15 are each formed from, forexample, an inorganic insulating material such as silicon oxide, siliconnitride or silicon oxynitride. The insulating film 13 is formed of, forexample, an organic insulating material such as polyimide. Note that theinsulating films 14 and 15 may be formed of an organic insulatingmaterial. In this embodiment, the insulating film 15 has a thickness(second thickness) T15, which is greater than a thickness (firstthickness) T14 of the insulating film 14. For example, the thickness T15is two times or more the thickness T14.

The first electrodes E1, the second electrode E2 and the third electrodeE3 are formed of, for example, a transparent conducting material such asindium tin oxide (ITO) or indium zinc oxide (IZO).

In this embodiment, the first electrode E1 and the third electrode E3are at the same potential. The second electrode E2 is at a potentialdifferent from that of the first electrode E1 and the third electrodeE3. For example, the common potential is supplied to the first electrodeE1 and the third electrode E3. A signal potential is supplied to thesecond electrode E2. That is, in this embodiment, the first electrode E1and the third electrode E3 function as the common electrode CE shown inFIG. 1. On the other hand, the second electrode E2 functions as thepixel electrode PE shown in FIG. 1. A fringing field for driving theliquid crystal layer LC is mainly formed by the second electrode E2 andthe third electrode E3 which oppose each other via the insulating film15. The capacitor for holding the signal potential is formed naturallybetween the second electrode E2 and the third electrode E3 which opposeeach other via the insulating film 15, and also between the firstelectrode E1 and the second electrode E2 which oppose each other via theinsulating film 14.

The second substrate SUB2 comprises an insulating substrate 20, alight-shielding layer 21, a color filters 22, an overcoat layer 23 andan alignment film AL2. The light-shielding layer 21 and the color filterlayer 22 are formed on a side of the insulating substrate 20, whichopposes the first substrate SUB1. The light-shielding layer 21 is formedof a resin colored in, for example, black and to prepare partitionedpixels PX. In the example illustrated, the light-shielding layer 21opposes the signal line S, the switching element SW, the contact holeCH3, etc. The overcoat layer 23 covers the color filter layer 22. Thealignment film AL2 covers the overcoat layer 23.

The first substrate SUB1 and the second substrate SUB2 described aboveare disposed such that the first alignment film AL1 and the secondalignment film AL2 oppose each other. Between the alignment film AL1 andthe alignment film AL2, a predetermined cell gap is formed with a spacerwhich is not illustrated. The cell gap is filled with the liquid crystallayer LC.

FIG. 4 is a plan view showing a configuration example of firstelectrodes E1 shown in FIG. 3. Each first electrode E1 overlaps aplurality of pixels PX arranged along the first direction X. Morespecifically, the first electrodes E1 each extend along the firstdirection X, and are arranged along the second direction Y at intervals.The first electrodes E1 are each formed into a belt-like shape havingsubstantially a constant width WE1. The width WE1 is less than a pitchP1 between adjacent scanning lines G. Here, the width WE1 and the pitchP1 are each defined along the second direction Y. The first electrode E1partially overlaps each of the respective scanning line G, therespective signal lines S, the respective semiconductor layers SC, andthe respective relay electrodes RE, but does not overlap the contactholes CH3. That is, the contact holes CH3 arranged along the firstdirection X are located between first electrodes E1 adjacent along thesecond direction Y.

FIG. 5 is a plan view showing a configuration example of secondelectrodes E2 shown in FIG. 3. The second electrodes E2 are arranged forthe pixels PX, respectively. That is, the second electrodes E2 arearranged in a matrix along the first direction X and the seconddirection Y. The second electrodes E2 overlap at least the relayelectrodes RE and the contact holes CH3, respectively. In the exampleillustrated, each of the second electrodes E2 has approximately arectangular shape comprising long sides along the second direction Y,and is formed over the entire region of each pixel PX. The secondelectrodes E2 each partially overlap the respective scanning lines G,but do not overlap the signal lines S. That is, each second electrode E2is arranged between the respective adjacent pair of signal lines S.

FIG. 6 is a plan view showing a configuration example of third electrodeE3 shown in FIG. 3. The third electrode E3 overlaps a plurality ofpixels PX arranged along the first direction X and the second directionY. For example, the third electrode E3 is formed from a single member.The third electrode E3 includes a plurality of openings OP in each pixelPX. These openings OP overlap each respective one of the secondelectrodes E2 shown in FIG. 5. The openings OP are located betweensignal lines S adjacent each other and between scanning lines G adjacenteach other, and arranged along the second direction Y at intervals. Theopenings OP do not overlap the relay electrode RE. In the exampleillustrated, the openings OP each have approximately a rectangular shapecomprising long sides along the first direction X. Because of thepresence of the openings OP, the area where the third electrode E3 andthe second electrodes E2 overlap each other is smaller than the areawhere the first electrodes E1 and the second electrodes E2 overlap eachother.

FIG. 7 is a plan view showing an example of arrangement of the firstelectrodes E1, the second electrodes E2, and the third electrode E3together with the potential supply line 6 shown in FIG. 1. Here, thesource driver 3, the gate drivers 4 a and 4 b, the signal lines S, thescanning lines G and the like are omitted from the illustration.

As described above, the potential supply line 6 is located on an outerside of the display area DA. That is, the potential supply line 6 iscloser to the end portions 2Xa, 2Xb, 2Ya and 2Yb of the display panel 2than the second electrodes E2 which functions as the pixel electrodesPE. In the example illustrated, the potential supply line 6 is patternedinto approximately a rectangle along the end portions 2Xa, 2Xb, 2Ya and2Yb. The potential supply line 6 comprises portions 6Xa and 6Xbextending along the first direction X, and portions 6Ya and 6Ybextending along the second direction Y. The second electrodes E2 arelocated on an inner side of the region surrounded by the potentialsupply line 6, and do not overlap the potential supply line 6.

The first electrodes E1 each extend along the first direction X, andinclude an end portion (second end portion) E1 a and an end portion(third end portion) E1 b on an opposite side to the end portion E1 a.The end portion E1 a overlaps the portion 6Ya of the potential supplyline 6. The end portion E1 b overlaps the portion 6Yb of the potentialsupply line 6. The third electrode E3 is provided over substantially theentire display area DA and overlaps at least the portions 6Ya and 6Yb.The first electrodes E1 and the third electrode E3 is connected to thepotential supply line 6 in a contact hole (first through-hole) CH4 aprovided in a position which overlaps the end portion E1 a and a contacthole (second through-hole) CH4 b provided in a position which overlapsthe end portion E1 b. Thus, a common potential is supplied to the firstelectrodes E1 and the third electrode E3 from the potential supply line6.

In this embodiment, the contact holes CH4 a and CH4 b are not providedin the display area DA. Therefore, along the first direction X, all thesecond electrodes E2 are located between the contact hole CH4 a and thecontact hole CH4 b.

FIG. 8 is a cross section taken along line VIII-VIII shown in FIG. 7.Here, only the first substrate SUB1 is shown. The end portion (first endportion) 2Ya of the display panel 2, described above, is equivalent toan end portion of the insulating substrate 10 included in the firstsubstrate SUB1. The potential supply line 6 is formed on the insulatingfilm 12 and covered by the insulating film 13 in the non-display areaNDA. The insulating film 13 includes the contact hole CH4 a whichpenetrates to the potential supply line 6.

The first electrode E1 extends along the first direction X and is formedin the contact hole CH4 a. The first electrode E1 is in contact with thepotential supply line 6 within the contact hole CH4 a. The insulatingfilm 14 and the insulating film 15 are not formed in the vicinity of thecontact hole CH4 a. The third electrode E3 extends along the firstdirection X, and is in contact with the first electrode E1 in thecontact hole CH4 a. Thus, the first electrode E1 and the third electrodeE3 are at the same potential as that of the potential supply line 6.Note that the structure in the vicinity of the contact hole CH4 b issimilar to that shown in FIG. 8, an explanation thereof will be omitted.

According to this embodiment, the first electrodes E1, the secondelectrodes E2, and the third electrode E3 are stacked on one another inthis order. The common potential is supplied to the first electrodes E1and the third electrode E3, and the signal potential is supplied to thesecond electrodes E2. The third electrode E3 comprises a plurality ofopenings OP, and forms a fringing field for driving the liquid crystallayer LC between the second electrodes E2 and themselves, respectively.On the other hand, the second electrodes E2 do not have openings, andeach are formed over substantially the entire pixels PX, respectively.Further, the first electrodes E1 are formed over the entire display areaDA except for the vicinities of the contact holes CH3. With thisstructure, even if a sufficient capacitor is not formed between thesecond electrodes E2 and the third electrode E3 due to theinsufficiently small overlapping area between the second electrodes E2and the third electrode E3, a sufficient storage capacitor for holdingthe signal potential between the first electrodes E1 and the secondelectrodes E2 can be formed.

Furthermore, according to this embodiment, the thickness T15 of theinsulating film 15 provided between the second electrodes E2 and thethird electrode E3 is greater than the thickness T14 of the insulatingfilm 14 provided between the first electrodes E1 and the secondelectrodes E2. Therefore, the capacitor formed between the secondelectrodes E2 and the third electrode E3 is less than the capacitorformed between the first electrodes E1 and the second electrodes E2.With this configuration, even if the size of the openings of the thirdelectrode E3 varies, in other words, if the overlapping area between thethird electrode E3 and the second electrodes E2 vary from one pixel PXto another, the adverse effect caused by the dispersion in thecapacitance formed between the third electrode E3 and the secondelectrodes E2 can be reduced. On the other hand, since the thickness T14of the insulating film 14 is decreased, a sufficient capacitance can beformed between the first electrodes E1 and the second electrodes E2.

Moreover, the coverage in the vicinities of the contact holes CH3 can beimproved by increasing the thickness T15 of the insulating film 15. Thatis, with the increased thickness T15 of the insulating film 15, theinsulation between the second electrodes E2 and the third electrode E3in the contact holes CH3 can be improved. Further, with the insulatingfilm 15 as such, discharge of the gas from the insulating film 13 formedof an organic insulating material can be suppressed.

Furthermore, according to this embodiment, the first electrodes E1 andthe third electrode E3 are connected to the potential supply line 6 onthe outer side of the display area DA. In other words, the contact holesCH4 a and CH4 b for connecting the first electrodes E1 and the thirdelectrode E3 to the potential supply line 6 are not provided in thedisplay area DA. With this structure, the common potential can besupplied to the first electrodes E1 and the third electrode E3 withoutreducing the aperture ratio of the display area DA.

As described above, according to this embodiment, a display device witha high definition can be obtained while maintaining display quality.

Modified examples of the first embodiment will be described withreference to FIGS. 9 to 14. FIG. 9 is a plan view showing a firstmodified example of the first embodiment. The first modified example isdifferent from the example shown in FIG. 6 in that the third electrodeE3 includes one opening OP in each pixel PX. The opening OP includes aportion OP1 extending along the first direction X and a portion OP2extending along the second direction Y. The disposition of the portionOP1 is similar to that of the opening OP shown in FIG. 6. The portionOP2 connects a plurality of portions OP1 arranged along the seconddirection Y.

In the first modified example as well, the second electrodes E2 to whichthe signal potential is supplied are formed between the first electrodesE1 and the third electrode E3, to which the common potential issupplied, and the thickness T15 of the insulating film 15 is greaterthan the thickness of the insulating film 14. Moreover, the firstelectrode E1 and the third electrode E3 are connected to the potentialsupply line 6 in the non-display area NDA. In the first modifiedexample, advantages effect similar to those of the example shown inFIGS. 1 to 8 can be obtained.

FIG. 10 is a plan view showing a second modified example of the firstembodiment. The second modified example is different from the exampleshown in FIG. 6 in that the openings OP of the third electrode E3 extendalong a direction where the first direction X and the second direction Ycross each other. For example, the openings OP are each formed intoapproximately a parallelogram and are arranged along the seconddirection Y. In the example illustrated, in each pair of pixels PXadjacent to each other in the first direction X, the extendingdirections of the openings OP are the same as each other. On the otherhand, in each pair of pixels PX adjacent to each other in the seconddirection Y, the extending directions of the openings OP are differentfrom each other. In the second modified example, advantages effectsimilar to those of the examples shown in FIGS. 1 to 8 can be obtained.

FIG. 11 is a plan view showing a third modified example of the firstembodiment. The third modified example is different from the exampleshown in FIG. 4 in that the signal lines S are crooked. The signal linesS each include bent portions SSa protruding in a direction opposite tothe first direction X and bent portions SSb protruding in the firstdirection X. The bent portions SSa and the bent portions SSb arearranged alternately along the second direction Y. Of the semiconductorlayer SC which constitutes the switching element SW, the first portionSC1 and the second portion SC2 extend along the respective signal linesS. For example, the relay electrodes RE each have a parallelogram shape.

In the third modified example, the first electrodes E1 are of a similarshape as that of the example shown in FIG. 4. That is, the firstelectrodes E1 extend along the first direction X, and are arranged alongthe second direction Y. The contact holes CH3 are located between thefirst electrodes E1 adjacent to each other in the second direction Y.

FIG. 12 is a plan view showing second electrodes E2 of a third modifiedexample of the first embodiment. The second electrodes E2 of the thirdmodified example embodiment are different from those of the exampleshown in FIG. 6 in that they are formed into a parallelogram shape. Thesecond electrodes E2 extend along the respective signal lines S. In eachrespective pair of pixels PX adjacent to each other in the firstdirection X, the extending directions of the second electrodes E2 arethe same as each other. On the other hand, in each respective pair ofpixels PX adjacent to each other in the second direction Y, theextending directions of the second electrodes E2 are different from eachother.

FIG. 13 is a plan view showing third electrode E3 of the third modifiedexample of the first embodiment. The third electrode E3 of the thirdmodified example embodiment are different from those of the exampleshown in FIG. 6 in that they include openings extending along therespective signal lines S. For example, the openings OP each have aparallelogram shape. The openings OP overlap respectively the secondelectrodes E2 shown in FIG. 12. In each respective pair of pixels PXadjacent to each other in the first direction X, the extendingdirections of the openings OP are the same as each other. On the otherhand, in each respective pair of pixels PX adjacent to each other in thesecond direction Y, the extending directions of the openings OP aredifferent from each other. In the example illustrated, the thirdelectrode E3 includes one opening OP in each pixel PX, but they mayinclude two or more openings. In the third modified example, advantageseffect similar to those of the examples shown in FIGS. 1 to 8 can beobtained.

FIG. 14 is a cross section showing a fourth modified example of thefirst embodiment. FIG. 14 is an enlarged view of the vicinities of thecontact holes CH3. The fourth modified example is different from theexample shown in FIG. 3 in that the insulating film 15 includes a firstlayer 151 and a second layer 152.

The first layer 151 covers the second electrodes E2 and is formed alsoon the insulating film 14. The second layer 152 is formed on the firstlayer 151. Further, in the example illustrated, the insulating film 15includes a third layer 153 located between the first layer 151 and thesecond layer 152. The third layer 153 is formed directly above thecontact holes CH3 to bury the concavities formed by the contact holesCH3.

For example, the first and second insulating films 151 and 152 are eachformed from, an inorganic insulating material such as silicon oxide,silicon nitride or silicon oxynitride. The third layer 153 is formedfrom, for example, an organic insulating material such as polyimide.

In the fourth modified example, advantages effect similar to those ofthe examples shown in FIGS. 1 to 8 can be obtained. Further, accordingto the fourth modified example, the concavities formed by the contactholes CH3 are buried by the third layer 153. Therefore, the unevenportion created in the vicinities of the second electrodes E2 due to theformation of the contact holes CH3 can be smoothed.

Second Embodiment

FIG. 15 is a cross section of a display device 1 according to the secondembodiment. The second embodiment is different from first embodiment inthat the signal potential is supplied to the first electrodes E1 and thethird electrode E3, and the common potential is supplied to the secondelectrodes E2. That is, the first electrodes E1 and the third electrodeE3 function as the pixel electrodes PE shown in FIG. 1. The secondelectrodes E2 function as the common electrodes CE shown in FIG. 1.

In the example illustrated, the switching elements SW are each atop-gate thin film transistor. The semiconductor layer SC is formed onthe insulating substrate 10, and is covered by the insulating film 11.The gate electrodes GE1 and GE2 are provided on the insulating film 11and are covered by the insulating film 12. The signal lines S and therelay electrodes RE are formed on the insulating film 12, and arecovered by the insulating film 13. The signal lines S and the insulatingfilm 12 are each in contact with the semiconductor layer SC in thecontact holes CH1 and CH2 which penetrate the insulating films 11 and12.

The insulating film 13 includes a contact hole CH3 which penetrates tothe relay electrode RE. The first electrodes E1 are formed on theinsulating film 13 and are provided also in the contact holes CH3 so asto be contact with the relay electrodes RE. The insulating film 14covers the first electrodes E1 except for the regions directly above thecontact holes CH3. In other words, the insulating film 14 uncovers thefirst electrodes E1 formed in the contact holes CH3. In the illustratedexample, the insulating film 14 is formed on the insulating film 13.

The second electrodes E2 are formed on the insulating film 14 except forthe vicinities of the contact holes CH3. The insulating film 15 coversthe second electrodes E2. The insulating film 15 covers the end portionof the second electrode E2, but it is not formed in the contact holesCH3. In other words, as in the case of the insulating film 14, theinsulating film 15 uncovers the first electrodes E1 formed in thecontact holes CH3. The third electrode E3 is formed on the insulatingfilm 15. The third electrode E3 extends into the contact holes CH3 to bebrought into contact with the first electrodes E1. Thus, the signalpotential supplied from the signal line S is supplied to the firstelectrode E1 and the third electrode E3 via the relay electrodes RE. Inthe example illustrated, the third electrode E3 includes a plurality ofslits SL. The slits ST each oppose the second electrodes E2,respectively. The third electrode E3 is covered by the alignment filmAL1.

The fringing field for driving the liquid crystal layer LC in thisembodiment is mainly formed by the second electrode E2 and the thirdelectrode E3 opposing each other via the insulating film 15. On theother hand, the capacitor for holding the signal potential is formed,naturally, by the second electrode E2 and the third electrode E3opposing each other via the insulating film 15, and also by the firstelectrode E1 and the second electrode E2 opposing each other via theinsulating film 14. In this embodiment as well, the thickness T15 of theinsulating film 15 is greater than the thickness T14 of the insulatingfilm 14. The other structure is similar to that of the first embodiment,and therefore an explanation therefor will be omitted.

FIG. 16 is a plan view showing a configuration example of firstelectrodes E1 shown in FIG. 15. The first electrodes E1 are disposed forthe respective pixels PX. That is, the first electrodes E1 are arrangedin a matrix in the first direction X and the second direction Y. Thefirst electrodes E1 overlap at least the relay electrodes RE and thecontact holes CH3, respectively. In the example illustrated, the firstelectrodes E1 each have approximately a rectangular shape with longsides along the second direction Y and are formed over the entirerespective pixels PX. The first electrodes E1 overlap the respectivescanning lines G partially, but do not overlap the signal lines S. Inother words, the first electrodes E1 are disposed between the signallines S adjacent to each other.

FIG. 17 is a plan view showing a configuration example of secondelectrodes E2 shown in FIG. 15. The second electrodes E2 each overlap aplurality of pixels PX arranged along the first direction X. Morespecifically, the second electrodes E2 each extend along the firstdirection X, and are arranged along the second direction Y at intervals.The second electrodes E2 are each formed into a belt-like shape havingsubstantially a constant width WE2. The width WE2 is less than the pitchP1 between the scanning lines G adjacent to each other. Here, the widthWE2 and the pitch P1 are each defined along the second direction Y. Thesecond electrodes E2 partially overlap the scanning lines G, the signallines S, the semiconductor layer SC and the relay electrodes RE,respectively, but do not overlap the contact holes CH3. In other words,the contact holes CH3 arranged along the first direction X are locatedbetween the second electrodes E2 adjacent to each other in the seconddirection Y.

FIG. 18 is a plan view showing a configuration example of thirdelectrodes E3 shown in FIG. 15. The third electrodes E3 are disposed inthe pixels PX, respectively. The third electrodes E3 are arranged in amatrix along the first direction X and the second direction Y.

The third electrodes E3 each include a contact portion E31, a connectionportion E32, and electrode portions E33. The contact portion E31overlaps all of the relay electrodes RE and the contact holes CH3. Thecontact portion E31 is connected to the respective relay electrode REvia the respective first electrode E1 in the respective contact holeCH3. The connection portion E32 is located immediately above therespective signal line S via the respective second electrode E2, andextends along the second direction Y from the contact portion E31. Theelectrode portions E33 each extend from the connection portion E32 alongthe first direction X. The electrode portions E33 overlap the secondelectrode E2 shown in FIG. 17. The electrode portions E33 are eachformed into a belt-like shape having substantially a constant width W33and arranged along the second direction Y at intervals. In the exampleillustrated, the third electrode E3 includes four electrode portionsE33, but the number of electrode portions E33 is not limited to this.The slits ST shown in FIG. 15 are each equivalent to the region betweenthe electrode portions E33 adjacent to each other. The third electrodesE3 each include the slits ST, and therefore the area where the thirdelectrode E3 and the second electrode E2 overlap each other is less thanthe area where the first electrodes E1 and the second electrodes E2overlap each other. Note that such a structure may as well be adoptedthat the connection portion E32 of each third electrode E3 is providedbetween signal lines S adjacent to each other in plan view.

FIG. 19 is a plan view showing an example of arrangement of the firstelectrodes E1, the second electrodes E2, and the third electrodes E3with the potential supply line 6 shown in FIG. 1. Here, the sourcedriver 3, the gate drivers 4 a and 4 b, the signal lines S, the scanninglines G and the like are omitted from illustration.

As in the case of the first embodiment, the potential supply line 6 islocated on an outer side of the display area DA. The potential supplyline 6 is closer to the end portions 2Xa, 2Xb, 2Ya and 2Yb of thedisplay panel 2 than the first electrode E1 and the third electrode E3,which function as pixel electrodes PE. The potential supply line 6 ispatterned into approximately a rectangle and comprises portions 6Xa and6Xb extending along the first direction X, and portions 6Ya and 6Ybextending along the second direction Y. The first electrode E1 and thethird electrode E3 are located on an inner side of the region surroundedby the potential supply line 6, and do not overlap the potential supplyline 6.

The second electrodes E2 each extend along the first direction X, andinclude an end portion (fourth end portion) E2 a and an end portion(fifth end portion) E2 b on an opposite side to the end portion E2 a.The end portion E2 a overlaps the portion 6Ya of the potential supplyline 6. The end portion E2 b overlaps the portion 6Yb of the potentialsupply line 6. The second electrodes E2 are connected to the potentialsupply line 6 in contact holes CH4 a and CH4 b provided in the positionswhich overlap the end portions E2 a and the end portion E2 b,respectively. Thus, the common potential is supplied to the secondelectrodes E2 from the potential supply line 6.

The contact holes CH4 a and CH4 b are not provided in the display areaDA. Therefore, along the first direction X, all of the first electrodesE1 and the third electrodes E3 are located between the contact hole CH4a and the contact hole CH4 b.

FIG. 20 is a cross section taken along the line XX-XX shown in FIG. 19.Here, only the first substrate SUB1 is shown. The potential supply line6 is formed on the insulating film 12 in the non-display area NDA, andis covered by the insulating film 13. The insulating film 13 includesthe contact hole CH4 a which penetrates to the potential supply line 6.The insulating film 14 covers the first electrodes E1 and is formed alsoon the insulating layer 13. In the example illustrated, the insulatingfilm 14 extends to the non-display area NDA, but it is not formed in thecontact hole CH4 a.

The second electrodes E2 are formed on the insulating film 14 and theinsulating film 13. The second electrodes E2 each extend along the firstdirection X, and are formed also in the respective contact holes CH4 a.The second electrodes E2 are brought into contact with the potentialsupply line 6 in the respective contact holes CH4 a. Thus, the secondelectrodes E2 and the potential supply line 6 are at the same potential.The insulating film 15 extends to the non-display area NDA, and coversthe second electrodes E2. The third electrodes E3 are formed on theinsulating film 15 and also immediately above the first electrodes E1,respectively. Note that the structure in the vicinity of each contacthole CH4 b is similar to that of FIG. 20, an explanation thereof isomitted.

According to this embodiment, the first electrode E1, the secondelectrode E2, and the third electrode E3 are stacked in this order. Thesignal potential is supplied to the first electrodes E1 and the thirdelectrodes E3, and the common potential is supplied to the secondelectrodes E2. The third electrodes E3 each include a plurality ofelectrode portions E33, and form a fringing field for driving the liquidcrystal layer LC between the second electrodes E2 and the electrodeportions themselves, respectively. On the other hand, the secondelectrodes E2 are formed over the entire display area DA except for thevicinities of the contact holes CH3. Moreover, the first electrodes E1are formed over substantially the entire pixels PX, respectively. Thus,even if the area of the region where the second electrodes E2 and thethird electrodes E3 overlap each other is small and a sufficientcapacitor is not formed between the second electrodes E2 and the thirdelectrodes E3 is not formed, a sufficient storage capacitance forholding the signal potential can be formed between the first electrodesE1 and the second electrodes E2. As a result, degradation of the holdingstate of the pixel signal in each pixel can be suppressed.

Moreover, as in the first embodiment, according to this embodiment, thethickness T15 of the insulating film 15 is greater than the thicknessT14 of the insulating film 14. Therefore, the capacitor formed betweenthe second electrodes E2 and the third electrodes E3 is smaller than thecapacitor formed between the first electrodes E1 and the secondelectrodes E2. Thus, even if the width W33 of the electrode portion E33of the third electrode E3 varies, the adverse effect due to thevariation in the capacitor formed by the third electrodes E3 and thesecond electrodes E2 in the respective pixels PX can be suppressed. Onthe other hand, with the reduced thickness T14 of the insulating film14, a sufficient capacity can be formed between the first electrodes E1and the second electrodes E2. Moreover, with the increased thickness T15of the insulating film 15, the coverage in the vicinities of the contactholes CH3 can be improved.

Further, according to this embodiment, the second electrodes E2 areconnected to the potential supply line 6 on an outer side of the displayarea DA. In other words, the contact holes CH4 a and CH4 b forconnecting the second electrodes E2 and the potential supply line 6 toeach other are not provided in the display area DA. With this structure,the common potential can be supplied to the second electrode E2 withoutreducing the aperture ratio of the display area DA.

As described above, according to this embodiment, a display device witha high definition can be obtained while maintaining display quality.

Modified examples of the second embodiment will be described withreference to FIGS. 21 to 25. FIG. 21 is a plan view showing a firstmodified example of the second embodiment. The first modified example isdifferent from the example shown in FIG. 18 in that the connectionportion E32 of each third electrode E3 does not overlap the signal linesS. In the example illustrated, the connection portions E32 are locatedin approximately a central portion between the signal lines S adjacentto each other.

In the first modified example as well, the second electrode E2 to whichthe common potential is supplied is formed between the first electrodesE1 and the third electrode E3, to which the signal potential issupplied, and the thickness T15 of the insulating film 15 is greaterthan the thickness of the insulating film 14. Moreover, the secondelectrodes E2 are connected to the potential supply line 6 in thenon-display area NDA. Thus, in the first modified example, advantageseffect similar to those of the examples shown in FIGS. 15 to 20 can beobtained.

FIG. 22 is a plan view showing a second modified example of the secondembodiment. The second modified example is different from the exampleshown in FIG. 18 in that the electrode portions E33 each extend along adirection crossing the first direction X and the second direction Y. Inthe example illustrated, the extending directions of the electrodeportions E33 are the same between pixels PX adjacent to each other inthe first direction X. On the other hand, in pixels PX adjacent to eachother in the second direction Y, the extending directions of theelectrode portions E33 are different from each other. In the secondmodified example as well, advantages effect similar to those of theexamples shown in FIGS. 15 to 20 can be obtained.

FIG. 23 is a plan view showing a third modified example of the secondembodiment. The third modified example is different from the exampleshown in FIG. 17 in that the signal lines S are crooked. The signallines S each include bent portions SSa projecting in a directionopposite to the first direction X, and bent portions SSb projecting inthe first direction X. The bent portions SSa and the bent portions SSbare arranged alternately along the second direction Y. Of thesemiconductor layer SC which constitutes the switching element SW, thefirst portion SC1 and the second portion SC2 extend along the signallines S, respectively. For example, the relay electrodes RE are eachformed into a parallelogram shape.

In the third modified example, the second electrodes E2 have a shapesimilar to that shown in the example shown in FIG. 17. That is, thesecond electrodes E2 each extend along the first direction X, and arearranged along the second direction Y. The contact holes CH3 are eachlocated between the second electrodes E2 adjacent to each other in thesecond direction Y.

FIG. 24 is a plan view showing first electrodes E1 in a third modifiedexample of the second embodiment. The first electrodes E1 in the thirdmodified example are different from those of the example shown in FIG.16 in that they are parallelograms. The first electrodes E1 each extendalong the respective signal lines S. In pixels PX adjacent to each otherin the first direction X, the extending directions of the firstelectrodes E1 are the same. On the other hand, in pixels PX adjacent toeach other in the second direction Y, the extending directions of thefirst electrode E1 are different from each other.

FIG. 25 is a plan view showing third electrodes E3 in a third modifiedexample of the second embodiment. The third electrodes E3 in the thirdmodified example are different from shoe of the example shown in FIG. 18in that they include electrode portions E33 extending along the signallines S. The third electrodes E3 do not include a connection portionE32, but the electrode portions E33 each extend from the respectivecontact portions E31. The electrode portions E33 each overlap therespective second electrodes E2 shown in FIG. 23. In pixels PX adjacentto each other in the first direction X, the extending directions ofelectrode portions E33 are the same. On the other hand, in pixels PXadjacent to each other in the second direction Y, the extendingdirections of electrode portions E33 are different from each other. Inthe example illustrated, the third electrodes E3 include one electrodeportion E33, but they may include two or more electrode portions E33. Inthe third modified example, advantages effect similar to those of theexamples shown in FIGS. 15 to 20 can be obtained.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. For example, in the embodiments described above, thestructure in which a liquid crystal layer is used as a display elementis adopted, but it is also possible to adopt such a structure which usesa material with some other optical properties, such as anelectrophoretic layer in place of a liquid crystal layer. Theaccompanying claims and their equivalents are intended to cover suchforms or modifications as would fall within the scope and spirit of theinventions.

What is claimed is:
 1. A display device comprising: a substrate; aswitching element provided on the substrate and including a relayelectrode; a first lower electrode provided further away from thesubstrate than the switching element, the first lower electrode havingan outer edge; a first insulating film provided on the first lowerelectrode; a first middle electrode provided on the first insulatingfilm, the first middle electrode connected to the relay electrodethrough a through hole of the first insulating film; a second insulatingfilm provided on the first middle electrode; and a first upper electrodeprovided on the second insulating film and supplied with a samepotential as that of the first lower electrode, the first upperelectrode including a plurality of openings, wherein the first middleelectrode functions as a pixel electrode, the first lower electrode andthe first upper electrode sandwich the first middle electrode andfunction as a common electrode, the through hole is provided outside theouter edge of the first lower electrode, an entirety of the thoroughhole is covered with the second insulating film and the first upperelectrode, and the second insulating film includes a filler disposed tofill in the through hole, and a first layer covering the through holeand the filler.
 2. The display device of claim 1, wherein an overlappingpart of the relay electrode overlaps the first lower electrode.
 3. Thedisplay device of claim 2, wherein a remaining part of the relayelectrode does not overlap the first lower electrode, and an area of theoverlapping part is smaller than an area of the remaining part.
 4. Thedisplay device of claim 1, further comprising: a second lower electrode,wherein both of the first lower electrode and the second lower electrodeare in a same layer, the second lower electrode is provided adjacent tothe first lower electrode, and the first middle electrode overlaps thefirst lower electrode, the relay electrode, and the second lowerelectrode.
 5. The display device of claim 4, wherein a space is providedbetween the outer edge of the first lower electrode and an outer edge ofthe second lower electrode, and the through hole is provided in thespace.
 6. The display device of claim 5, wherein the first lowerelectrode, the second lower electrode, and the space are covered withthe second insulating film and the first upper electrode.
 7. The displaydevice of claim 5, wherein the switching element includes a gateelectrode, and the gate electrode overlaps the second lower electrode,and does not overlap the first lower electrode.
 8. The display device ofclaim 7, wherein the gate electrode, the first lower electrode, thesecond lower electrode, and the space are covered with the secondinsulating film and the first upper electrode.
 9. The display device ofclaim 4, further comprising: a display area including the first middleelectrode and provided on the substrate; a surrounding area defining thedisplay area; and a potential supply line provided on the substrate inthe surrounding area, wherein the first lower electrode, the secondlower electrode, and the first upper electrode are connected to thepotential supply line.
 10. The display device of claim 9, wherein eachof the first lower electrode and the second lower electrode extends fromone side of the surrounding area to another side of the surrounding areaacross the display area, and the first upper electrode covers anentirety of the display area and a part of the surrounding area.
 11. Thedisplay device of claim 10, wherein the first lower electrode, thesecond lower electrode, and the first upper electrode overlap at least apart of the potential supply line at the surrounding area in plan view.12. The display device of claim 11, wherein the first lower electrode,the second lower electrode, and the first upper electrode are connectedto the potential supply line at the one side and another side of thesurrounding area.
 13. The display device of claim 1, further comprising:a display area including the first middle electrode and provided on thesubstrate; a surrounding area defining the display area; and a potentialsupply line provided on the substrate in the surrounding area, whereinthe first lower electrode and the first upper electrode are connected tothe potential supply line.
 14. The display device of claim 13, whereinthe first lower electrode extends from one side of the surrounding areato another side of the surrounding area across the display area, and thefirst upper electrode covers an entirety of the display area and a partof the surrounding area.
 15. The display device of claim 14, wherein thefirst lower electrode and the first upper electrode overlap at least apart of the potential supply line at the surrounding area in plan view.16. The display device of claim 15, wherein the first lower electrodeand the first upper electrode are connected to the potential supply lineat the one side and another side of the surrounding area.
 17. Thedisplay device of claim 1, wherein the second insulating film comprisesa second layer covering the first middle electrode, the first layerlocated above the second layer, and the filler located between thesecond layer and the first layer and overlapping the through hole. 18.The display device of claim 17, wherein the first layer and the secondlayer are formed of an inorganic insulating material, and the filler isformed of an organic insulating material.
 19. The display device ofclaim 1, wherein the second insulating film is thicker than the firstinsulating film.
 20. The display device of claim 19, wherein a thicknessof the second insulating film is two times or more a thickness of thefirst insulating film.